Protein nutrition sometimes needs to be adapted to specific metabolic and physiologic conditions, e.g. because persons suffering from an allergy cannot accept certain proteins, or persons suffering from a disorder in amino acid metabolism need supplementation with specific amino acids or need to avoid specific amino acids. For example, Phenylketonuria (PKU) patients often need a lifelong feeding which is low in phenylalanine, and patients suffering from cow's milk allergy are often fed amino acid-based formulas to manage gastrointestinal problems due to food protein allergy.
In those cases, protein nutrition is adapted by providing blends of amino acids or peptides. Such blends may also contain or be combined with other food components such as vitamins, minerals, carbohydrates or lipids. Typically, such products have a powder-like form, which can be reconstituted to a drink or allows admixture with drinks.
However, such powder-like forms cause several problems. Many amino acids are poorly palatable because of bad taste. For example the branched chain amino acids leucine, isoleucine, valine, threonine, the acid amino acids glutamic acid and aspartic acid, tyrosine, phenylalanine, histidine, tryptophan and cysteine are poorly soluble, have bad organoleptic properties or may interact with other components in the mixture-giving rise to poor taste and appearance. Also, particles of such amino acids in dry form may have different sizes, which may cause inhomogeneities in the final product due to a varying degree of settlement during storage. Very small particles, may cause a dust when the package is opened or the powder is transferred.
Numerous ways of manufacturing dry or semi-dry products that comprise a large amount of free amino acids have been suggested. In most cases the synthetic ingredients are obtained in dry form which are either blended in dry form or dissolved in an aqueous phase, optionally together with other ingredients, optionally blended with a lipid phase, homogenised, heat-treated and evaporated and spray-dried to produce a powder which could also be agglomerated. Such agglomerates consist of powder particles, which comprise all ingredients which have been spray-dried and which typically include digestible carbohydrates, vitamins a lipid phase and minerals.
For example, to obtain a stable amino acid preparation not having a smell, a taste and an unpleasant texture after taking, not causing any side effect, JP 58216118 teaches the mixing of an amino acid with 10-30 wt % of higher fatty acids, waxes, carbowaxes, triglycerides (e.g. stearic acid, bees wax, polyethylene glycol 4000, Witepsol), which are solid at normal temperature and are pharmacologically permissible. After melting and homogenising, the mixture is solidified. However, it requires large amounts of these fatty acids to end up with an acceptable taste improvement, thus disadvantageously increasing the dosage in situations where the uptake is often already causing problems. Consumption of large amounts of fatty acids and waxes may also be undesired for health reasons. The products, or their spray-dried counterparts, develop Maillard products during production or storage, and interactions may occur between reactive amino acids and vitamins.
Although U.S. Pat. No. 6,506,422 mentions the use of encapsulated amino acids for administration to phenylketonuria patients, in fact it discloses ground mixtures of amino acids and fats with the aforementioned problems. Example 4, concerning encapsulated amino acids, only describes simple mixing of amino acids and fat mix at 70° C., homogenization and cooling to 30° C. However, such a process would not yield satisfactory shielding of the bad-tasting amino acids. Further, the so called encapsulation in U.S. Pat. No. 6,506,422 only involves a limited amount of amino acids, i.e. lysine, methionine, tryptophan and valine. The cooled fat-treated mixture is added to another amino acid mixture. Hence, the formula thus prepared may be suitable for admixture with drinks, it would exude an odour and/or taste which would be noticeable in every meal due to the fact that many components will interact on reconstitution as they are not coated, giving an unpleasant taste. Even if pleasant, its dominant taste and odour will eventually annoy a patient sentenced to lifelong administration of such nutritional formula, especially since he or she must take considerable quantities of the phenylalanine-free mixture of amino acids with his or her meals.
Moreover, U.S. Pat. No. 6,506,422 states that lecithins may be present in the composition, for establishing stability during reconstitution in hot water. The lecithin does not contribute to the stability of the encapsulated product. With lecithin high amounts of polyunsaturated fatty acids are introduced, which will easily oxidise during shelf life, thus disadvantageously resulting in off-flavours and potential toxic reaction products.
JP 2042967 provides a non-lipophilic substance, for instance an amino acid or crude drug, with a coating by attaching a surfactant and a phospholipid to the surface of the substance, and applying oil and fat exhibiting crystalline state at normal temperature (e.g. palm oil or beef tallow) to the surface. The surface of the substance coated with the oil and fat film is then coated with a phospholipid (e.g. lecithin) dissolved in a solvent (e.g. ethanol), and the solvent is removed to easily perform the coating of the substance and mask the disagreeable taste and odour of the substance. Again, the resulting coated substance disadvantageously involves multiple layers with phospholipids, especially lecithin.
EP-A-363.879 uses a gelling agent for encapsulation of amino acids and mentions that hard fat may be used for encapsulation to mask the taste and to prolong the life of the amino acids in the stored product. It is clear from the examples that a vitamin-mineral premix is coated together with the amino acids. Apparently, the solution given there is not considered satisfactory, since the composition further contains dried or candied fruit. It is the inventors' findings that this may well be caused by interactions between amino acids and other active ingredients, such as the micronutrients.
US-A-2003/148013 discloses the use of zinc stearate as a coating material for amino acids and micro nutrients. This product solves the problem of leaching. Also here, lecithin is one of the mentioned fats for use in the coating material.
EP-A-388.237 describes compositions comprising lecithin as an emulsifier, thereby denying the problem of deterioration of the coating. Furthermore, nothing is done to prevent contact between micronutrients and amino acids either.
Hence, there is a need for a dry or semi-dry free amino acid-containing nutritional supplement having a homogeneous particle size distribution, which product has a neutral taste and comprises low amounts of off-flavours and deterioration of active components, allowing acceptable admixture with foodstuffs.